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The rear lighting and signaling system of automotive vehicles was considered to be one component of the traffic system which was amenable to development to provide improvements in driver performance and, hence, in accident reduction. The problem was discussed in the context of primary and augmenting cue utilization by drivers. Various display techniques were systematically investigated employing number, functional separation, and color coding in addition to intensity and flash coding now used. A static driving simulation and actual driving tests showed that number coding, functional separation, and color were effective in reducing following driver response time, missed signals, and errors. Ratings of signal system effectiveness correlated well with objective data. Studies concerned with color discrimination and visibility in clear and fog atmospheres showed that green-blue would be practical presence light color.

The measurement of drivers' performance at the limit of capability is difficult due to methodological problems, moment to moment variability of drivers, differences between drivers, and their interactions with the characteristics of the vehicle, road, and environment. Aspects of longitudinal and lateral vehicle control are discussed by reference to results of braking and steering tests, with emphasis on the variations between the performance of drivers. The effectiveness of drivers in vehicle braking is shown to be a function of the brake system deceleration/pedal force gain. Overall braking performance could also be improved by increasing the abilities of drivers who are poor in this task, by training in brake modulation on dry and wet pavements. The best drivers are as effective as an antilocking brake system, except on the equivalent of ice covered pavement. In steering control drivers increase their response frequency bandwidth as task difficulty increases.

Drivers carried out a lane-changing and passing maneuver using convex and plane exterior mirrors alone or in combination with a plane interior mirror. The data showed that the addition of the plane interior mirror compensated for judgmental errors found when convex mirrors were used alone. When the speed difference was 15 mph between the overtaking car and the subject's car, subjects accepted gaps that were too short irrespective of the exterior mirror type. The data suggested that exterior convex mirrors of radii greater than 30 in. may be used reasonably safely by drivers and would have the advantage of providing a considerably increased field-of-view compared to currently used exterior mirrors.

Surveys of rear lighting system malfunctions on passenger cars and light trucks showed that about 4% of vehicles with single compartment rear lamps had an inoperative presence or stop/turn lamp, while less than 1% of vehicles with multiple compartment rear lamps had at least one operating presence lamp compartment working on each side, and about 2.5% had no stop/turn signal lamp compartments operating on one side. Thus, although the frequency of failure of bulbs or circuits was greater in rear lighting systems with multiple compartment than single compartment lamps, the likelihood that at least one presence or signal lamp compartment will be operating on each side of the vehicle is greater in lighting systems with multiple compartment lamps, by 2-3%. The effects of some rear lighting system malfunctions on the ability of drivers to identify signals was evaluated in two experiments using a driving simulator.

A laboratory simulation of dawn/dusk illumination showed that following vehicles could be detected equally well in plane and convex mirrors, and a night driving test showed that low- and mid-beam headlamps of a following car produced discomfort glare responses that were independent of whether the exterior mirror was plane or convex. Visibility of the following car was rated better with the plane exterior mirror. Measures of performance of drivers relevant to safety in lane changing and passing were not different when they used a plane or convex exterior mirror in conjunction with a plane interior mirror, and did not differ in the day or at night. When the initial speed of the overtaking car was 15 mph (24 km/h) greater than the subjects' car, drivers significantly underestimated the relative speed, indicating a potential cause of collisions with a following vehicle in lane changing and passing maneuvers.

The eye fixations were measured of two motorcyclists who drove a motorcycle and later an automobile on two-lane rural roads at about 45 mph, in daytime. The effects of road edge delineation, road geometry, oncoming vehicles, and whether the drivers were controlling a motorcycle or an automobile were evaluated in terms of the manner in which the drivers used their eyes to obtain visual information. The results indicated that most of the drivers' attention was directed within 5° of the forward line of sight, but on curves, the drivers' eye fixations shifted in the direction of the curve. When an oncoming vehicle appeared, the drivers spent a substantial proportion of the viewing time looking at it periodically. The mean duration of glances were longer for these drivers when operating a motorcycle than an automobile.

A computer simulation of a nighttime meeting between two vehicles is described, including results showing the correspondence between predicted visibility distances and those obtained in field tests. The simulation is used to compare visibility distances and glare effects in meetings between vehicles equipped with the U.S. low beam, European low beam, and an experimental mid beam, in various conditions of aim. Results of this study suggest that differences between European and U.S. low beams are of little practical consequence. By comparison, the mid beam appears to offer a potentially improved meeting beam, pending resolution of problems of rearview mirror glare, beam switching, etc.

The literature on headlamp aiming is surveyed in detail to pinpoint the various sources and magnitudes of aim variance. Four major sources of variance are identified (differences between beam and mounting plane, photometric changes in use, long axis alignment, and human factors), along with a number of others of lesser consequence. Illustrations are offered showing the expected population variance under a variety of conditions. It is apparent that, at the present state-of-the-art, a substantial percentage of the lamp population can be expected to be beyond the limits recommended in SAE J599c. It is further apparent that this would be true regardless of whether or not a vehicle inspection program is in operation. Recommendations are given regarding research emphasis in headlighting. Ways of reducing variance from the most significant sources are considered and recommendations offered.

Differences in characteristics between automobiles and trucks, such as driver eye height and headlamp mounting height, were examined, as well as roadway vertical and horizontal curvature and meeting beam patterns and lamp aim. Effects of these variables were evaluated by a computer simulation of nighttime meetings on a 2-lane road. The visibility distance and direct and indirect (mirror) glare discomfort effects were measured. Results suggest that: low beam headlamps on trucks should not be mounted at more than about 36 in (0.91 m) from ground level, the increase in visibility provided by the mid beam is less for truck drivers than those of automobiles, the mid beam is less affected by vertical aim variations than the low beam, the mid beam should be extinguished by the vehicle in the inside lane on curves when meeting other vehicles and when following another vehicle at less than about 200 ft (61 m).

The paper reviews some of the underpinnings of the research that was done that led to adoption of the high mounted brake lamp. The expected reduction in rearend collisions of 50%, attributable to the lamp, has not been realized. Most recently, a reduction of 4% was reported. This large difference between the predicted effectiveness of the safety device with its actual effect is disturbing. The paper attempts to show the reasons for the low effectiveness which include a lack of evidence for the high-mounting location, overriding an SAE standard on the intensity of high-mounted rear signal lamps and no valid theory of driver performance.

This paper presents the results of a study directed toward examining the effects of glare resulting from following headlights reflected in rearview mirrors. In particular, the effects of different driving environments are discussed with regard to their effects on glare. The results of a computer analysis predicting the magnitude of glare reflected from rearview mirrors for several headlight systems are also presented. These computations cover a range of intercar spacings and both inside and outside mirrors. An important question is also posed concerning the effects of glare in a driver's peripheral field-of-view and its potential effects on the detection of early warning events.